Herpes simplex virus detection by ELISA: effect of enzyme amplification, nature of lesion sampled and specimen treatment

Diagnosis of Herpes Simplex Virus: Laboratory and Point-of-Care Techniques

Herpes is a widespread viral infection caused by the herpes simplex virus (HSV) that has no permanent cure to date. There are two subtypes, HSV-1 and HSV-2, that are known to cause a variety of symptoms, ranging from acute to chronic. HSV is highly contagious and can be transmitted via any type of physical contact. Additionally, viral shedding can also happen from asymptomatic infections. Thus, early and accurate detection of HSV is needed to prevent the transmission of this infection. Herpes can be diagnosed in two ways, by either detecting the presence of the virus in lesions or the antibodies in the blood. Different detection techniques are available based on both laboratory and point of care (POC) devices. Laboratory techniques include different biochemical assays, microscopy, and nucleic acid amplification. In contrast, POC techniques include microfluidics-based tests that enable on-spot testing. Here, we aim to review the different diagnostic techniques, both laboratory-based and POC, their limits of detection, sensitivity, and specificity, as well as their advantages and disadvantages.

Rapid detection, culture-amplification and typing of herpes simplex viruses by enzyme immunoassay in clinical samples

BACKGROUND

The laboratory diagnosis of herpes simplex infection may require rapid (direct) tests, as well as cell cultures, for detection of the virus in clinical samples. The quantity of virus present in clinical samples is variable and this may depend on the period from onset of rash. In addition, not all patients may show obvious symptoms with this infection. The successful culture of herpes simplex virus requires prompt transportation after collection of the specimen as the virus is easily inactivated. Hence, rapid and culture tests would enable detection of non-viable and viable viruses.

STUDY DESIGN

We describe the rapid detection of HSV by EIA directly in various clinical samples using commercially available polyclonal sera. In addition specimens were inoculated in microwell cell cultures and 4 days post inoculation the culture fluids were tested for HSV and subtyped by a similar EIA (culture amplified EIA).

RESULTS

The direct EIA showed an endpoint detection of 100 TCID50/ml, sensitivity of 92% (all specimen types) and specificity of 100%. The direct EIA sensitivity was 97% in non-genital specimens and 88% in genital specimens. The culture amplified EIA showed a sensitivity of 95% compared to all confirmed HSV positive samples.

CONCLUSIONS

The results of the HSV rapid tests were available within 24 h from receipt of specimens. Specimens which were culture negative/direct EIA positive were confirmed by blocking antisera. Culture positive specimens which were direct EIA negative were confirmed by subtyping of the virus.

Quantitative determination and visualization of herpes simplex virus type 1 antigen, free and cell-bound by ELISA

A method of quantifying and visualizing herpes simplex virus type 1 antigen by indirect enzyme-linked immunosorbent assay (ELISA) is described. This assay is simplified by the use of polyclonal serum and can be applied to the quantification of free antigen as well cell-bound. Moreover, cell viral antigen can be visualized. Antigen sources were viral suspensions, infected cells and proteins extracted from infected cells. The assay was specific and its sensitivity was dependent on the antigen source. The technique was regarded as specific within a range showing a direct correlation (r > 0.8) between the concentration of the antigen and the net absorbance value (the difference of the absorbance obtained with the viral antigen minus the control antigen). The technique has advantages over other ELISA procedures: does not require monoclonal antibodies, or labelled antiviral immunoglobulins or antiviral serum from two different species. In addition total free antigen can be measured.

The digoxigenin:anti-digoxigenin (DIG) technology--a survey on the concept and realization of a novel bioanalytical indicator system

A review is given on the novel non-radioactive digoxigenin:anti-digoxigenin (DIG) bioanalytical indicator system. After a general introduction on direct and indirect indicator systems based on previous non-radioactive indicator reactions as well as in vitro and in vivo amplification procedures the principle of the new digoxigenin:anti-digoxigenin technology is demonstrated. The novel system is based on the specific high-affinity interaction between the cardenolide digoxigenin from Digitalis plants and a digoxigenin-specific antibody coupled with a reporter group. A variety of methods for digoxigenin modification of nucleic acids, proteins and glycans are presented. In addition, various applications of the novel non-radioactive indicator system in a variety of direct or indirect detection approaches with either insoluble or soluble substrates are described. It is also shown that with these applications alternative reaction formats are used which are partly characterized by additional amplification steps.

Comparison of two enzyme-linked immunosorbent assays for detection of herpes simplex virus antigen

Two enzyme-linked immunosorbent assays (ELISAs) for herpes simplex virus (HSV) detection were compared with culture in a prospective, blinded study with 153 patients with suspected recurrent oral or genital HSV. A subset of 15 of these subjects were studied daily until symptom resolution during a single episode of recurrent HSV. Direct-site specimens were collected and either placed in viral transport media (for Ortho ELISA and fresh inoculation into primary rabbit kidney cells) or frozen in ELISA collection media (DuPont). One hundred eighty-six culture-ELISA comparisons were analyzed. On the basis of culture positivity, the DuPont and Ortho ELISAs differed substantially with regard to sensitivity (93 versus 35%) but had similar specificities (95 versus 100%) and positive (85 versus 100%) and negative (98 versus 85%) predictive values. There were seven DuPont ELISA-positive, culture-negative samples which were confirmed positive for HSV by blocking antibody test (revised specificity, 100%; positive predictive value, 100%). Six of these discrepant samples were from previously culture-positive subjects. These results demonstrate that currently available ELISA kits vary substantially as to their sensitivities in detecting HSV antigen from direct-site specimens. In addition, antigen detection, by ELISA technology, is not always synonymous with state of viral infectivity as judged by tissue culture cytopathic effect.

Detection and direct typing of herpes simplex virus by polymerase chain reaction

A method for the detection and direct typing of herpes simplex virus (HSV) by the polymerase chain reaction (PCR) technique has been developed. One common upstream primer and two type-specific downstream primers were prepared to amplify DNA from the HSV type 1 and type 2 DNA polymerase gene. Using these three primers simultaneously in the PCR reaction mixtures, both types of HSV DNA were amplified to produce products of different sizes. By direct gel analysis, the products of standard HSV type 1 and type 2 strains had the predictive sizes of 469 and 391 base pairs, respectively, and the difference in molecular mass enabled us to type the HSV strain. A total of 24 strains (type 1; 16 and type 2; 8 strains) were examined by PCR, and the results were consistent with those determined by immunofluorescence using type-specific monoclonal antibodies. No specific amplification was observed using other herpes virus or human genomic DNAs. The PCR method was then applied to clinical specimens. Of 15 samples obtained from oral lesions of children with herpetic gingivostomatitis, all (100%) were HSV positive by PCR, compared with 13 (86.7%) using standard cell culture methods. Three specimens from vulvar lesions of women with genital herpes were positive using both PCR and cell cultures. There was complete agreement in the typing of HSV strains using the PCR method or virus isolation. On the basis of these results, it is suggested that DNA amplification and typing by PCR is particularly useful for material from which virus isolation might be difficult.

Non-radioactive labeling and detection of nucleic acids. I. A novel DNA labeling and detection system based on digoxigenin: anti-digoxigenin ELISA principle (digoxigenin system)

A novel highly sensitive non-radioactive DNA labeling and detection system based on the ELISA principle has been developed. DNA is modified with the cardenolide-hapten digoxigenin by enzymatic incorporation of digoxigenin-labeled deoxyuridine-triphosphate with Klenow enzyme. Digoxigenin is linked to dUTP via an 11-atom linear spacer (Dig-[11]-dUTP). Following hybridization of membrane-bound target-DNA with a digoxigenin-labeled probe, the hybrids are detected by an ELISA reaction using digoxigenin-specific antibodies covalently coupled to the marker enzyme alkaline phosphatase [(Dig):CIAP]. This binding of antibody: marker enzyme-conjugate is followed by an enzyme-catalysed coupled redox reaction with the colour substrates 5-bromo-4-chloro-3-indolyl phosphate (BCIP) and nitroblue tetrazolium salt (NBT) giving rise to a deep-blue coloured, water-insoluble precipitate directly adhering to the membrane. The digoxigenin system allows the detection of 0.1 pg homologous DNA within 16 h in dot- and Southern-blots on nitrocellulose or nylon membranes avoiding any significant background even after a prolonged period of color development. Due to its high sensitivity and specificity, the new system is appropriate for detection of single-copy genes in genomic blots as well as for Northern, slot, colony, plaque and in situ hybridizations.

Simplified test for detecting the resistance of herpes simplex virus to acyclovir

The detection of herpes simplex virus (HSV) antigen by means of an enzyme amplified ELISA was investigated for rapid screening of acyclovir (ACV) resistance. Vero cell monolayers were inoculated in the presence of different concentrations of ACV. When cytopathic effect was present, the culture supernatants were tested by ELISA. The absorbance values were found to correlate with the results of virus yield and plaque reduction assays. The comparison between absorbance values obtained in the presence of 10 microM ACV and in the absence of drug provided the basis for a simplified sensitivity test. The use of a single ACV concentration allowed discrimination between ACV-resistant and ACV-sensitive reference strains, the detection of ACV-resistant virus mixed in the proportion of 10% with ACV-sensitive virus, and a study of the emergence of an ACV-resistant virus population in serial samples taken from experimental rabbit keratitis. The simplified susceptibility assay is a sensitive and convenient method for rapid screening of HSV resistance to ACV.

Evaluation of an enzyme immunoassay for the detection of herpes simplex virus (HSV) antigen from clinical specimens in viral transport media

A total of 301 clinical specimens (229 culture positive and 72 culture negative) were assayed retrospectively by an enzyme immunoassay. Specimens were transported to the virus lab in viral transport media (VTM), and were inoculated into HF and A549 cell culture tubes for viral isolation with the remainder of the sample being saved at -70 degrees C. Specimens were thawed, vortexed and resuspended in 10 x Herptran concentrate and each sample was then added in duplicate to designated wells of a microtiter plate for the EIA assay. The EIA detected 147/150 (98%) culture positive specimens from symptomatic patients, 63/79 (79.7%) culture positive specimens from patients considered asymptomatic and 210/229 (91.7%) culture positive specimens overall. The EIA was negative for 70/72 (97.2%) culture negative specimens. These data suggest that the EIA test can be used with clinical specimens submitted in conventional VTM. However, VTM samples which are EIA negative, particularly with EIA values close to the EIA positive cutoff value, need to be cultured.

Comparison of colorimetric, fluorescent, and enzymatic amplification substrate systems in an enzyme immunoassay for detection of DNA-RNA hybrids

The monoclonal antibody solution hybridization assay is a novel enzyme immunoassay for detection of RNA with a biotinylated DNA probe. To increase the sensitivity of this test, a fluorescent substrate and an enzymatic amplification cycling system were compared with a conventional colorigenic substrate for alkaline phosphatase. The fluorescent, cycling, and colorigenic substrates detected, respectively, 10, 10, and 100 amol of unbound alkaline phosphatase in 2 h. With a prolonged incubation period of 16.6 h, the conventional substrate measured 10 amol of the enzyme. In the immunoassay for RNA detection, the fluorescence and cycling assays were faster than that using the colorigenic substrate and reached an endpoint sensitivity of 3.2 pg/ml (0.16 pg per assay) of cRNA. However, longer incubation periods (16.6 h) for optimal generation of the colorigenic product led to a comparable level of sensitivity for the conventional substrate.

Diagnosis of herpes simplex virus infection in a clinical setting by a direct antigen detection enzyme immunoassay kit

A commercial 4-h direct herpes simplex virus (HSV) antigen detection enzyme immunoassay (EIA) kit (Du Pont Herpchek) was evaluated by using 273 clinical specimens obtained in a hospital-based infectious disease practice. The EIA was compared with a standard culture method in which WI38 cells were inoculated within 20 min of sample collection. Cultures were observed for 2 weeks, and positive findings were confirmed by fluorescein-labeled monoclonal antibody (FA) staining. The values for the overall HSV detection rate were 40.7% by the standard culture method and 41.4% by EIA. In eight cases, the EIA was positive, while the culture method was negative; however, clinical data and confirmatory blocking EIA suggested that a true HSV infection was present. For six FA-confirmed, culture-positive samples, the direct EIA was negative; however, an EIA performed on the supernatants of these cultures was positive, suggesting that the failure of the EIA to detect these samples was not due to lack of strain specificity of the test. After confirmatory tests of standard culture and EIA discrepant results, the overall sensitivity of the test was 95.0% (113 of 119) and the specificity was 100% (154 of 154).

Clinical laboratory applications of monoclonal antibodies

Monoclonal antibody (MAb) technology is well recognized as a significant development for producing specific serologic reagents to a wide variety of antigens in unlimited amounts. These reagents have provided the means for developing a number of highly specific and reproducible immunological assays for rapid and accurate diagnosis of an extensive list of diseases, including infectious diseases. The impact that MAbs have had in characterizing infectious disease pathogens, as well as their current and future applications for use in clinical microbiology laboratories, is reviewed. In addition, the advantages (and disadvantages) of the use of MAbs in a number of immunoassays, such as particle agglutination, radioimmunoassays, enzyme-linked immunosorbent assays, immunofluorescent-antibody assays, and immunohistology, are explored, including the use of these reagents in novel test system assays. Also, nucleic acid probe technology is compared with the use of MAbs from the perspective of their respective applications in the diagnosis of infectious disease agents. There is no question that hybridoma technology has the potential to alter significantly the methods currently used in most clinical microbiology laboratories.

Rapid amplified enzyme linked immunosorbent assay evaluated for detecting herpes simplex virus

A new amplified enzyme linked immunosorbent assay (amplified ELISA) kit for detecting herpes simplex virus (HSV) antigen was evaluated. Duplicate swabs were taken from 180 patients with clinically suspected herpes lesions. Tests were performed on a direct swab extract and viral transport medium containing a swab. Of the 93 culture positive specimens, 78 of the extracted samples (sensitivity 83.9%) and 72 of the swabs in transport medium (sensitivity 77.4%) were positive by amplified ELISA. A higher sensitivity (49/54, 90.7%) was obtained when the extracted swab was taken first. In early lesions the sensitivity was 93.8% but in late lesions it was 73.3%. This ELISA therefore offers an alternative to culture for early lesions, but culture is the method of choice for differential diagnosis of genital ulceration. As the specificity was 94.3%, this test is acceptable for testing populations with a high prevalence of HSV infection, but culture should be used for screening populations in which the disease is rare.

The selection and performance of monoclonal and polyclonal anti-respiratory syncytial virus (RS) antibodies in capture ELISAs for antigen detection

Six monoclonal antibodies directed against fusion protein (F) or nucleoprotein (NP) of respiratory syncytial virus (RS) have been investigated in an antigen capture ELISA for virus detection. The potency, spectrum and pattern of reactivity were investigated with the intention of selecting antibodies reacting with RS-common antigen determinants and with complementary rather than competitive activity. Two anti-F protein antibodies satisfied these criteria and were used with enzyme amplified detection in a two site monoclonal assay (MCA/MCA) or as detectors with a polyclonal antibody as capture (PCA/MCA). Comparative studies were performed with immunofluorescence (FA) as the reference test and nasopharyngeal aspirates processed in different ways. The PCA/MCA assay was superior to that using monoclonal antibodies alone and gave results comparable to the reference method. However, the apparent sensitivity related to FA varied with the type of sample processing used. These results emphasise the need for a critical analysis of the factors which can influence the sensitivity of a particular assay system before judgements on relative sensitivity are made.

Rapid diagnosis of herpes simplex virus infections in conventional and shell vial cell cultures using monoclonal antibodies

One hundred specimens for herpes simplex virus (HSV) isolation were tested in parallel by conventional and by centrifugation-enhanced cell culture, followed by identification using monoclonal antibodies to HSV-1 and HSV-2. Sensitivity was comparable by the two methods; conventional culture was only marginally slower and was easier to fit into the routine of a busy laboratory. It is, therefore, advocated for HSV detection in clinical specimens.